A good deal of research is done in windtunnels, although there are much more sophisticated techniques than looking at smokestreams.

There are paints which change color (under blacklight, IIRC) depending on the temperatures, pressures, and shears it is exposed to. Shear and pressure differential sensors can be built into the models. Lasers can be used to measure flow velocities. The list goes on and on.

The other side of the spectrum comes with computational fluid dynamics, or CFD. These are high powered (and high priced) software packages which simulate fluid flow conditions.

Staff: Mentor

Re: Aerodynamics

Originally posted by Thomas1980 Which methods or tools is there for scientists who work with aerodynamics? Only windtunnels with smoke sticks (and watertanks) and computersimulations based on calculations?

Well, when you're studying aerodynamics with a wing, there are two things you could do. You could (either with a real or virtual model) move fluid about the wing, or move the wing through the fluid. The windtunnels and watertanks are tools for when the wing is stationary. The other way then, of course, would be trialling with real aircraft (or whatever is in subject) -- scaled models, RC planes, prototype builds, etc.

Originally posted by Thomas1980
Which methods or tools is there for scientists who work with aerodynamics? Only windtunnels with smoke sticks (and watertanks) and computersimulations based on calculations?

If I may turn your question around a bit

Instead of asking what tools we need to do to get the job done, it is more instructive in this instance to ask what jobs we need to get done, and therefore what tools

First, you have Fluid Dynamics as applied to buildings. A big field, because it determines how strong your supports for billboards have to be, whether your skyscraper is going to sway too much or whether your smoke stack is going to fall down. Here, atmospheric data are collected from weather stations spanning decades and are statistically compiled & correlated. Yes, there's a small chance that your skyscraper will fall down because of a freak gust, but the design here is always statistically done. Just a small chance . At times, wind tunnel models of scaled down cities are even created! Then you also have computation modelling here.

Naval architecture, such as oil rigs and more recently, offshore tidal power platforms, require similar attention. The tools here are often simple theory for rough calculations, followed up by water tank experiments.

Then, you have Fluid Dynamics as applied to aircraft surfaces and geometry. For here, you have subsonic and supersonic flight. In subsonic flight, most establishments can have the cheaper subsonic windtunnels. For supersonic components, you have 'gun' tubes and even supersonic windtunnels. Some establishments choose to use exotic gases and cryogenic windtunnels to obtain similarity parameter (Reynolds number) matching, basically by trying to lower the viscosity. For obvious reasons, supersonic wind tunnels require huge quantities of energy to run and can not usually be run for sustained periods. Flow parameters are measured or indirectly inferred using things such as smoke, dyes in liquids, interferometry, Schlieren imaging (exclusively for supersonic flows), pressure probes, force balances.

You also have Fluid Dynamics as applied to turbomachinery, such as jet engines. In this instance, the flow is almost always turbulent with at least some supersonic regions. Theory takes you so far, usually by analysing the thermodynamics of the engine and various aspects such as Cascade Theory and Blade Element Theory. After that, it is empiricism, experiement and computation.

As a sidenote, Aero Engineering is much more than just Aerodynamics. There is cutting edge material science with the exciting stuff like monocrystalline turbine blades; composites; titanium, aluminium and steel alloys. Not boring concrete like civil engineers study . It also has Materials modelling, which covers aspects such as Fracture mechanics and composite failure. Then there are Structural analysis aspects, which covers things like how thick your fuselage skin has to be and how many/how stiff your ribs/stringers should be. Design aspects, where you use CAD, theory and calculations to turn an aircraft into something tangible on paper. Then there are manufacturing aspects, where you turn it into reality...things like superplastic forming of Titanium alloys and forging of work-hardened components. This is even before you decide to do your Masters or PhD in Turbulence modelling, Ballistics, Supersonic Aerodynamics, Space Vechicle Design, Plasma Aerodynamics, Advanced Composites, Wing-In-Ground Effect.

Rocket science isn't called the hardest subject and frequently used as a 'very-difficult-subject' label for nothing

Thank you very much indeed for your thorough answer.
My interest is mostly in the tools, since I probably wont work much with aerodynamics in its pure form as you describe it.. I've just got an idea for an aerodynamicsanalyser, and Im currently checking if its already been invented... So therefor I'll ask a bit more about these tools:
What is interferometry and Schlieren imaging? The rest of the methods in your reply are either selfexplainatory or explained by my memory combined with your description...
And what about getting windtunneldata into your pc for calculations? How can you do that?
Thank you for your time and answers.

Schlieren imaging makes use of the fact that there are typically discontinuous density changes in supersonic flows. The idea is that because of this, you can 'see' such discontinuities because they would also have an associated discontinuity in optical refractive index.

Velocity interferometry relies on measuring the changes in frequency of reflected or scattered light, with the Doppler shift being used to infer velocity.

Getting windtunnel data into the computers is usually automated, and isn't a problem. You either write your own program to do the data logging for you or just buy one off the shelf and configure it. Or, you could always make it into an 'experiment' and get a poor undergrad sod to do it for you

Again thank you for your reply, very useful infortation. Still regarding the collection of data, how does it "get into" the computer? Data from a windtunnel with smoke, how do you load that into the computer? I know it looks great, but I can't understand how that kind of experiments can be registered and analysed... Only way I can think of is trial and error with models... Doesn't sound very "hitech" IMHO.
Thanks again.

I have noticed that my room fan collects dust aerodynamically on its blades, "improving" the original airfoil. Is there an analogous process of deposit used in practical experiment to your knowledge?

Hmm...I don't know about whether dust on your room fan improves its blades or not. My fan does that as well . I guess the closest analogue to this which happens "IRL" would be ice build-up on aerofoils in operation on aircraft. It actually reduces the lift coefficient (on average by ~60% IIRC) and reduces the stall angle up to several degrees.

My guess is that the effect on the aerofoil lift is due to the reduction in curvature of the aerofoil. Ice accretion is proportional to the rate of flow of air over a given surface and the surface's ability to absorb heat from budding ice crystals. So it would seem that ice build up occurs more on the upper surfaces of the aerofoil and possibly more in regions with curvature. The reduction in stalling angle is probably due to the smooth properties of ice, which would result in a more easily separated laminar shear layer vs. a turbulent one.

As for an actual experiment that does something similar, apart from the ice build up thing, I can't think of one offhand.

Originally posted by Thomas1980 Again thank you for your reply, very useful infortation. Still regarding the collection of data, how does it "get into" the computer? Data from a windtunnel with smoke, how do you load that into the computer? I know it looks great, but I can't understand how that kind of experiments can be registered and analysed... Only way I can think of is trial and error with models... Doesn't sound very "hitech" IMHO.
Thanks again.

Using undergrad students to record experiments usually involves just a clipboard, pen and, if you're feeling kind, a keyboard

Smoke in the windtunnel is usually used for what is known as "flow visualisation", i.e. as an instructive tool. But if someone wants to automatically read values off them, setting up the apparatus to measure things like smoke streamline separation changes, etc. could possibly involve some kind of optical device. For other things like pressure readings, you can get digital pressure gauges that would just electronically register their readings with a data input card installed on the computer.